Electron discharge device with current surge attenuating resistance



. Dec. 27, 1966 A. v. GALLARO ET AL WITH CURRENT SURGE ELECTRON DISCHARGE DEVICE ATTENUATING RESISTANCE 2 Sheets-Sheet 1 Filed June 27, 1963 INVENTORS Amlwny K Gal/arc John J Miller ATTORNEY A. v. GALLARO ET AL 3,295,008 ELECTRON DISCHARGE DEVICE WITH CURRENT SURGE ATTENUATING RESISTANCE 2 Sheets-Sheet 2 i MW Dec. 27, 1966 Filed June 27, 1963 MW II 7 INVENTORS Amhany 1 Gal/am 1 Jb/m J: Miller ATTORNEY 10 OHMS 3.- ATTfNUAT/NG RES/574N65- 5' RES/STANCE OHMS 3,295,008 ELEQTRON DISCHARGE DEVICE WITH CNT SURGE ATTENUATING RESISTANCE Anthony V. Gallaro, Auburn, and John J. Miller, Seneca Falls, N.Y., assignors to Sylvania Electric Products Inc.,

a corporation of Delaware Filed June 27, 1963, Ser. No. 291,131 8 Claims. (Cl. 3153) This invention relates to electron discharge devices and more particularly to current surge attenuating resistance means for cathode ray tubes.

Conventional cathode ray tubes are usually high voltage operating devices consisting of an electron beam source and an electron impinging surface suitably contained within an evacuated envelope. The electron beam source, or electron gun, includes several high voltage and low voltage electrodes arranged in specific relationship with each other to facilitate the acceleration and focussing of the electron beam on the screen or electron impinging surface. The large difference in voltage between the high voltage electrodes and the low voltage electrodes of the electron beam source increases the probability of severe dielectric breakdown therebetween with the possible subsequent generation of large current surges. This condition is aggravated by sharp edges, deviations in critical spacings, and alignment of the electrodes within the electron gun structure. These current surges emanating within the cathode ray tube can effect damage to external components in the associated tube circuitry in addition to possible internal destruction within the tube with subsequent resultant loss of emission and damage to the electron impinging surface. High current surges also aggravate the formation of electrical leakage paths resulting from metal vaporization and sputtering of electrode material onto adjacent insulating members of the electron beam source.

A current surge of one microsecond duration may be of sufficient magnitude to produce deleterious effects. For example, a cathode ray tube operating at kv. and having a screen plus envelope capacitance of 0.002 microfarads has the capability of producing forty amperes average current with peak currents many times this value.

Several methods have been proposed to minimize or reduce the deleterious effects of these current surges in cathode ray tubes. These methods require protective impedances to be added in those external circuits most subject to current surges, or utilize a high impedance coating on discrete areas of the inner surface of the cathode ray tube envelope. Adding protective impedances in the vulnerable external circuitry adds cost and does not adequately provide the desired protection for the electron beam source since protection is considerably removed from the point of current surge generation. Adding a high impedance coating on discrete areas of the inner surface of the cathode ray tube envelope complicates the manufacturing operation since the area to be coated must first be cleaned of all previous manufacturing residues to insure adequate electrical continuity and coating adherence thereon.

Accordingly, an object of this invention is to provide a cathode ray tube having built-in provision for attenuating current surges.

Another object of this invention is to provide a current surge attenuating resistance close to the source of such surge.

Yet another object of this invention is to accomplish such current surge attenuation in an economical manner.

A still further object of this invention is to provide a current surge attenuating resistance utilizing materials Patented Dec. 27, 1966 and technology consistent with established cathode ray tube manufacturing practice.

The foregoing objects are achieved in one aspect of this invention by the provision of a cathode ray tube whose electron beam source is electrically connected to the final anode coating through a snubber arrangement incorporating a section of current surge attenuating resistance material.

For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a typical cathode ray tube;

FIGS. 2, 3, 4, and 5 are views showing several embodiments of the invention;

FIG. 6 is a graph showing the relationship of attenuating resistance values versus one microsecond current surges.

FIG. 7 is a graph illustrating attenuating resistance values versus percent attenuation of one microsecond current surges.

Referring to FIG. 1, there is shown a cathode ray tube 11 of the type commonly used in dynamic visual display apparatus wherein an electron beam source 23 is suitably positioned within an envelope 13 having a face plate 15 compatibly joined to a substantially funnel shaped body 16 having a neck portion 17. A cathodoluminescent screen or electron impinging surface 19 suitably disposed on the inner surface of face plate 15 is excited by an electron beam 21 emanating from the electron beam source 23. This electron beam source is a conventional cathode ray tube gun structure having'a plurality of interrelated components, i.e.: a thermionic cathode assembly 25 providing the primary source of electrons for electron beam 21, a first grid 27 providing electron control or modulation, a second grid 29 effecting electron acceleration and shielding, a first anode 31 coupled to a second anode 35 facilitating a high voltage electrode accelerating means, a fourth grid 37 spacedly telescoping the anodes effecting focussing of the electron beam 21 upon the impinging surface 19, and a plurality of insulating support members 33, one of which is shown in 'FIG. 1, holding the aforementioned gun components in precise axial and spatial relationship with each other. On the inner surface of the funnel portion 16 of envelope 13 there is suitably disposed, in a manner conventional to the art, a film of electrically conductive material such as colloidal graphite or vaporized aluminum forming a final anode coating 39. External electrical connection to this coating is facilitated by a connector button 43 hermetically sealed into the wall of the funnel portion 16 of envelope 13. As further illustrated in FIG. 1, the.

. nector button 43. An external source, not shown, supplies high voltage to button 43. Final anode coating 39, envelope 13, and external conductive coating 45 form the plates and dielectric of a capacitor 47 connected to ground 49 to provide filtering for the external high voltage supply.

First anode 31 and second anode 35 constitute the high voltage accelerating electrodes of electron beam source 23. Thermionic cathode assembly 25, first grid 27, second grid 29, and fourth grid 37 constitute the low voltage electrodes of the electron beam source 23. Associated circuitry of the low voltage electrodes, for the sake of simplicity, is indicated by resistors 67, 69, 71, and 73.

The foregoing tube shown in FIG. 1 illustrates the general construction of a typical electron discharge device whose included electron beam source, even with normal manufacturing tolerances, may have considerable variation in electrode axial alignment and spatial relationship. In addition, electrodes of the electron beam source 23 may exhibit rough surfaces or jagged edges thereby enhancing corona or are discharge malfunctions with subsequent current surgase in the electron beam source and associated circuitry as indicated by resistors 67, 69, 71, and 73. The aforementioned current surge is sustained by the filter capacitor 47 of which the final anode coating 39 forms a plate. The final anode coating is coupled to the high voltage electrode 35 by the connecting snubbers 41 whereby a generated current surge is carried to the electron beam source 23 and associated circuitry resistors 67, 69, 71, and 73 with possible deleterious effects.

This invention teaches the interposition of a current surge attenuating resistance between the filter capacitor plate disposed on the inner surface of envelope 13, also referred to as final anode coating 39, and the source of the generated are or current surge in the electron beam source 23 in such a manner as to attenuate the current surge to values harmless to the electron beam source, electron impinging surface, and associated tube circuitry. Applicable current surge attenuating resistances for incorporation in the various embodiments of the invention to be hereinafter described may be selected from a number of suitable materials such as, for example, iron oxide, chrome oxide, aluminum oxide, lead oxide, copper oxide, silicon dioxide, titanium dioxide, barium titanate, strontium titanate, barium-strontium titanate, resistive carbon compounds, and nickel-chromium alloys.

FIG. 2 shows one embodiment of a snubber means 41 constituting an electrically conductive member 51 having a high voltage electrode attachment portion 53, a final anode contact portion 55, and a current surge attenuating resistance material 57 selected from the aforementioned listing of applicable materials. This resistance may be applied to the final anode contact portion 55 in the form of a coating, lamination, winding, layer, or section to perform the desired function of current surge attenuation. The high voltage electrode attachment portion 53 may be atfixed to the high voltage electrode 35 by suitable bonding means such as spot welding or insertion into slots or retaining arrangements integral to the high voltage electrode 35.

FIG. 3 illustrates another embodiment of this invention in which the snubber means 41 consists of an electrically conductive member 51 wherein both the high voltage electrode attachment portion 53 and final anode contact portion 55 incorporate a section of aforementioned current surge attenuating resistance material 57. In this embodiment the high voltage electrode attachment portion 53, with attenuating resistance material disposed thereon, is aflixed to the high voltage electrode 35 by conventional means such as an integral slot or other suitable retaining arrangement not shown.

FIG. 4 shows yet another embodiment of this invention whereby the snubber means 41 has included therein a modified electrically conductive member 51 incorporating a section of aforementioned current surge attenuating resistance material 57 whereby means for current surge attenuation is provided between high voltage electrode attachment portion 53 and final anode contact portion 55.

It may be desired to contain the resistance material in a ceramic or glass retaining structure 61 with suitable end closures 63 to provide structural support and electrical securement. The end closures 63 may be of a glass or ceramic material such as Sauereisen manufactured by the Sauereisen Cements Company of Pittsburgh, Pennsyl- Vania.

FIG. 5 illustrates an additional embodiment of this invention in which the snubber means 41 consists of an electrically conductive member 51 having a high voltage electrode attachment portion 53 and a final anode contact portion 55. The high voltage electrode attachment portion 53 is bonded to a substantially collar-shaped snubber supporting structure 65 which is made of current surge attenuating resistance material 57. In this embodiment of the invention the current surge attenuating resistance material 57 may be one of the numerous nickelchromium alloys commercially available as, for example, Nichrome manufactured by Driver-Harris Company of Harrison, New Jersey. Snubber means supporting structure 65 is welded or otherwise affixed to the high voltage electrode 35.

FIG. 6 is a graph comparing current surge attenuating resistance versus corresponding one-microsecond-current surge values for several specified operating voltages at one capacitance Value. These curves show that 10 ohms limit the current surges to very low values in the order of milliamperes for a tube operating with 200 m.m.f. capacitance in a broad operating range of 2 to 40 kv. As illustrated by the curves, a resistance of 500 ohms begins to attenuate the current surges to relatively low values in the case of a tube operating at 2 kv. but does not sufiiciently attenuate for a tube operating at 40 kv. The one-microsecond-current, or attenuated current surges, shown in FIG. 6 are derived from the following relationship.

attenuated current= where E is the tube operating voltage and R is the current surge attenuating resistance in ohms. It is to be noted that the attenuated current is dependent upon E and R only, except that the maxmum current surge is a function of the charge on capacitor 47 and current surge duration. This latter relationship may be expressed by maximum current surge= where E is the tube operating voltage, C is the envelope capacitance in farads, and T is the duration of the current surge expressed in seconds. From the foregoing discussion a safe current surge attenuating resistance covering normal cathode ray tube operating voltages and capacitances can therefore be reduced to at least 5000 ohms.

FIG. 7 graphically illustrates current surge attenuating resistance versus percent attenuation for a conventional range of cathode ray tube capacitances. This figure shows that 10 ohms gives practically attenuation of current surges for capacitance values shown, which considered in conjunction with FIG. 6 defines a reasonable range of current surge resistance values for tube functioning at diverse operational voltages and capacitances. To be more explicit, a cathode ray tube operating at 20 kv. with a 2000 m.m.f. envelope capacitance incorporating a 10 ohm current surge attenuating resistance and experiencing one-microsecond-current surge will now be attenuated to 20 milliamperes as compared to 40 amperes without the resistance feature. This is a reduction of 2000:1, or an attenuation of 99.95 percent. The method of determining percent attenuation as shown in FIG. 7 is ascertained from the following equation:

R 100(C'R T) Percent attenuat-ron- E X100- where E is the tube operating voltage, C is the envelope capacitance expressed in farads, T is the current surge duration in seconds, and R is the attenuating resistance in ohms. Since E cancels out of the equation, it is to be noted that percent attenuation does not depend upon operating voltage but rather upon envelope capacitance, attenuating resistance, and cur-rent surge duration. From the foregoing discussion it has been found desirable to specify a 90 percent attenuation or better for commonly used cathode ray tubes.

It is readily evident from the preceding explanations that the current surge attenuating resistance is most advantageously interposed between the filter capacitor 47, which sustains the current surge, and the electron beam source 23 where dielectric breakdown is most likely to occur. This resistance serves to attenuate current surges to permissive values prior to their reaching low voltage electrodes 25, 27, 29, and 37 and associated circuitry indicated by resistors 67, 69, 71, and 73.

The invention can readily be incorporated in present day cathode ray tube manufacturing operations alleviating the necessity for special care or preparation of the envelope 13 or final anode coating 39. The envelope can be prepared by present day techniques well known to the industry. The current surge attenuating resistance material may be disposed on currently available snubbers by such means as dipping, spraying, brushing, winding, laminat ing, bonding, or clamping as indicated in the foregoing il lustrated embodiments of this invention.

The materials used in this invention are, in general, commonly used in cathode ray tube manufacturing with their out-gassing properties and other characteristics well known to those skilled in the art.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. An electron discharge device having an envelope, an electron beam source and an electron impinging surface comprising:

a high voltage electrical conductive coating disposed upon the inner surface of said envelope;

a high voltage electrode associated with said electron beam source and spaced from said high voltage electrical conductive coating;

a low voltage electrode in spaced relationship with said high voltage electrode in said electron beam source;

electrical connective snubber means coupling said high voltage electrode with said high voltage electrical conductive coating; and

current surge attenuating resistance material incorporated as an integral part of said electrical connective snubber means.

2. An electron discharge device according to claim 1 wherein said attenuating resistance material has a resistance magnitude of at least 5000 ohms.

3. An electron discharge device according to claim 1 wherein said attenuating resistance material provides at least 90 percent attenuation of discharge surge currents.

4. A cathode ray tube having an envelope, an electron beam source and an electron impinging surface comprismg:

a high voltage electrical conductive final anode coating disposed on the inner surface of said envelope;

a high voltage accelerating electrode constituting a high voltage element of said electron beam source;

a low voltage electrode in spaced relationship with said high voltage electrode, said low voltage electrode forming a low voltage element of said electron beam source; and

snubber means formed to provide electrical connection between said high voltage electrode and said final anode coating, said snubber means comprising an electrically conductive member; and

a section of current surge attenuating resistance material incorporated in said snubber means.

5. A cathode ray tube having an envelope, an electron beam source and an electron impinging surface comprismg:

a high voltage electrical conductive final anode coating disposed on the inner surface of said envelope;

a high voltage accelerating electrode constituting a high voltage element of said electron beam source;

a low voltage electrode in spaced relationship with said high voltage electrode, said low voltage electrode forming a low voltage element of said electron beam source;

snubber means formed to provide electrical connection between said high voltage electrode and said final anode coating, said snubber means comprising an electrically conductive member having a high voltage electrode attachment portion and a final anode contact portion; and

a current surge attenuating resistance material disposed on said final anode contact portion.

6. A cathode ray tube having an envelope, an electron beam source and an electron impinging surface comprisa high voltage electrical conductive final anode coating disposed on the inner surface of said envelope;

a high voltage accelerating electrode constituting a high voltage element of said electron beam source;

a low voltage electrode in spaced relationship with said high voltage electrode, said low voltage electrode forming a low voltage element of said electron beam source;

snubber means formed to provide electrical connection between said high voltage electrode and said final anode coating, said snubber means comprising an electrically conductive member having a high voltage electrode attachment portion and a final anode contact portion; and

a current surge attenuating resistance material disposed on said high voltage electrode attachment portion and on said final anode contact portion of said snubber means.

7. A cathode ray tube having an envelope, an electron beam source and an electron impinging surface comprismg:

a high voltage electrical conductive final anode coating disposed on the inner surface of said envelope;

a high voltage accelerating electrode constituting a high voltage element of said electron beam source;

a low voltage electrode in spaced relationship with said high voltage electrode, said low voltage electrode forming a low voltage element of said electron beam source;

snubber means formed to provide electrical connection between said high voltage electrode and said final anode coating, said snubber means comprising an electrically conductive member having a high voltage electrode attachment portion and a final anode contact portion; and

a section of a current surge attenuating resistance material incorporated in said conductive member intermediate said high voltage electrode attachment portion and said final anode contact portion.

8. A cathode ray tube having an envelope, an electron beam source and an electron impinging surface comprismg:

a high voltage electrical conductive final anode coating disposed on the inner surface of said envelope;

a high voltage accelerating electrode constituting a high voltage element of said electron beam source;

a low voltage electrode in spaced relationship with said high voltage electrode, said low voltage electrode forming a low voltage element of said electron beam source;

snubber means formed to provide electrical connection between said high voltage electrode and said final anode coating, said snubber means comprising an 5 electrically conductive member having a high voltage electrode attachment portion and 'a final anode contact portion; and

snubber means supporting structure comprising a ourtachment portion of said snub'ber means being discretely bonded thereto to provide electrical connection between said high voltage electrode and said final anode coating.

References Cited by the Examiner UNITED STATES PATENTS 2,829,292 4/1958' De Vere Krause 31382 rent surge attenuating resistance material formed for 10 JAMES LAWRENCE Primary Examiner compatible peripheral bonded engagement with said high voltage electrode, said high voltage electrode at- P. C. DEMEO, Assistant Examiner. 

1. AN ELECTRON DISCHARGE DEVICE HAVING AN ENVELOPE, AN ELECTRON BEAM SOURCE AND AN ELECTRON IMPINGING SURFACE COMPRISING: A HIGH VOLTAGE ELECTRICAL CONDUCTIVE COATING DISPOSED UPON THE INNER SURFACE OF SAID ENVELOPE; A HIGH VOLTAGE ELECTRODE ASSOCIATED WITH SAID ELECTRON BEAM SOURCE AND SPACED FROM SAID HIGH VOLTAGE ELECTRICAL CONDUCTIVE COATING; A LOW VOLTAGE ELECTRODE IS SPACED RELATIONSHIP WITH SAID HIGH VOLTAGE ELECTRODE IN SAID ELECTRON BEAM SOURCE; ELECTRICAL CONNECTIVE SNUBBER MEANS COUPLING SAID HIGH VOLTAGE ELECTRODE WITH SAID HIGH VOLTAGE ELECTRICAL CONDUCTIVE COATING; AND CURRENT SURGE ATTENUATING RESISTANCE MATERIAL INCORPORATED AS IN INTEGRAL PART OF SAID ELECTRICAL CONNECTIVE SNUBBER MEANS. 